16.19. Additional Protocol I extends the categories of persons and objects against whom reprisals are prohibited to:

This means that reprisals taken in accordance with the statement are permissible by and against the United Kingdom. However, commanders and commanders-in-chief are not to take reprisal action on their own initiative. Requests for authority to take reprisal action must be submitted to the Ministry of Defence and require clearance at Cabinet level. 

It is prohibited … to make [historic monuments, works of art or places of worship which constitute the cultural or spiritual heritage of peoples] … the object of reprisals … Because of its wording, the prohibition … only applies to very important cultural property of international stature … Property loses its protection if it is used for military purposes. 

To be lawful, a belligerent reprisal must meet two conditions. First, it must not be directed against persons or objects against which the taking of reprisals is specifically prohibited … Additional Protocol I prohibits the taking of reprisals against historic monuments (Article 53(c)) … The application of these provisions would have a greater effect on the retaliatory use of nuclear weapons. Again, however, these provisions are correctly regarded as innovative and thus as inapplicable to the use of nuclear weapons. 

The obligations of Articles 51 and 55 are accepted on the basis that any adverse party against which the United Kingdom might be engaged will itself scrupulously observe those obligations. If an adverse party makes serious and deliberate attacks, in violation of Article 51 or Article 52 against the civilian population or civilians or against civilian objects, or, in violation of Articles 53, 54 and 55, on objects or items protected by those Articles, the United Kingdom will regard itself as entitled to take measures otherwise prohibited by the Articles in question to the extent that it considers such measures necessary for the sole purpose of compelling the adverse party to cease committing violations under those Articles, but only after formal warning to the adverse party requiring cessation of the violations has been disregarded and then only after a decision taken at the highest level of government. Any measures thus taken by the United Kingdom will not be disproportionate to the violations giving rise thereto and will not involve any action prohibited by the Geneva Conventions of 1949 nor will such measures be continued after the violations have ceased. The United Kingdom will notify the Protecting Powers of any such formal warning given to an adverse party, and if that warning has been disregarded, of any measures taken as a result.